1. Field of the Invention
The present invention relates to a settling time acquisition method. More specifically, it relates to a method of acquiring a settling time of a deflection amplifier for electron beam shaping deflection in an electron beam writing apparatus.
2. Description of Related Art
The lithography technique that advances miniaturization of semiconductor devices is extremely important as being a unique process whereby patterns are formed in semiconductor manufacturing. In recent years, with high integration of LSI, the line width (critical dimension) required for semiconductor device circuits is decreasing year by year. For forming a desired circuit pattern on such semiconductor devices, a master or “original” pattern (also called a mask or a reticle) of high accuracy is needed. Thus, the electron beam (EB) writing technique, which intrinsically has excellent resolution, is used for producing such a high-precision master pattern.
FIG. 10 is a conceptual diagram for explaining operations of a variable shaped electron beam writing or “drawing” apparatus. The variable shaped electron beam writing apparatus operates as described below. A first aperture 410 has a quadrangular opening 411 for shaping an electron beam 330. A second aperture 420 has a variable-shape opening 421 for shaping the electron beam 330 having passed through the opening 411 of the first aperture 410 into a desired quadrangular shape. The electron beam 330 emitted from a charged particle source 430 and having passed through the opening 411 is deflected by a deflector to pass through a part of the variable-shape opening 421 of the second aperture 420, and thereby to irradiate a target object or “sample” 340 placed on a stage which continuously moves in one predetermined direction (e.g., the X direction) during the writing. In other words, a quadrangular shape that can pass through both the opening 411 and the variable-shape opening 421 is used for pattern writing in a writing region of the target object 340 on the stage continuously moving in the X direction. This method of forming a given shape by letting beams pass through both the opening 411 of the first aperture 410 and the variable-shape opening 421 of the second aperture 420 is referred to as a variable shaped beam (VSB) system.
When performing writing in a writing apparatus, a charged particle beam such as an electron beam is deflected by a deflector, where a DAC (digital/analog converter) amplifier is used for deflecting the beam. Beam deflection using the DAC amplifier serves, for example, for controlling the shape and size of a beam shot, controlling the position of a beam shot, and blanking of a beam. For performing the beam deflection, it is necessary to set the settling time of a DAC amplifier required to accurately execute deflection of a set displacement amount. If a settling time is insufficient, an error occurs in the deflection movement amount. If a settling time is too long, the throughput degrades. Therefore, it is desirable to set a settling time as short as possible within the range where no error occurs.
With high accuracy and miniaturization of a circuit pattern typified by semiconductor devices in recent years, high accuracy and high throughput are also needed for the electron beam writing apparatus. Conventionally, optimization of a settling time with respect to beam deflection for controlling a shot position has attracted attention, wherein is performed to measure a writing position with a position measuring device and set a settling time within the range which can be measured by the position measuring device and in which no positional deviation is generated (refer to, e.g., Japanese Patent Application Laid-open (JP-A) No. 2010-074039). In connection with the high accuracy and high throughput, deflection regions and shaping beam maximum shot sizes have been miniaturized. Moreover, figure sizes have also been miniaturized due to the miniaturization of patterns. Therefore, it has become required to optimize and accurately set a settling time in shaping deflection, which has not been much focused, especially in changing a figure size.